Field
The disclosed concept pertains generally to power bus apparatus and, more particularly, to power systems including an alternating current or direct current power bus. The disclosed concept also pertains to indicator apparatus for an alternating current or direct current power bus.
Background Information
Inside of electrical control centers, as well as other electrical environments, there are bus bar wiring conductors and lugged cable connection conductors, as well as conductor taps for three-phase power. This is true regardless whether the corresponding electrical product is for low voltage or for medium voltage.
Maintenance personnel can be harmed when accidentally touching energized surfaces of power bus bars.
Electrical sensors of various types are used to detect the current flowing through a conductor. Such sensors include, for example, a single Hall effect sensor that produces an output voltage indicative of the current magnitude as well as more conventional current sensors such as a shunt resistor or a current transformer.
Hall effect devices have been used to sense variations in magnetic flux resulting from a flow of current through a conductor. Some of these known devices have used a flux concentrator to concentrate magnetic flux emanating from the flow of current through the conductor. It has previously been suggested that electrical current sensing apparatus could be constructed in the manner disclosed in U.S. Pat. Nos. 4,587,509; and 4,616,207.
It is also known to measure the current in a conductor with one or two appropriately placed Hall sensors that measure flux density near the conductor and to convert the same to a signal proportional to current. See, for example, U.S. Pat. Nos. 6,130,599; 6,271,656; 6,642,704; and 6,731,105.
U.S. Pat. No. 7,145,322 discloses a power bus current sensor, which is powered by a self-powered inductive coupling circuit. A sensor senses current of the power bus. A power supply employs voltage produced by magnetically coupling the power bus to one or more coils, in order to power the sensor and other circuitry from flux arising from current flowing in the power bus.
U.S. Patent Application Pub. No. 2007/0007968 discloses a system for monitoring an electrical power system including one or more transducer units, each of which has a current measuring device and a voltage measuring device coupled to a respective one of the phase conductors of the power system, and a transducer wireless communications device. The transducer unit includes a battery for providing power to the components thereof. The battery is connected to a trickle charger, which, in turn, is electrically coupled to a phase conductor. The trickle charger is a known parasitic power charger that draws power from the phase conductor and uses it to charge the battery.
A known prior proposal for monitoring a bus bar wiring conductor employs a current transformer to harvest energy or an associated signal, through coupling to the magnetic field caused by current flowing through the conductor. However, if a load is not connected to the conductor, and, thus, no current is flowing, then a current transformer (or magnetic coupling) will not function.
U.S. Patent Application Pub. No. 2013/0076520 discloses an indicator system for an alternating current power bus. The system comprises: an electret operatively associated with the alternating current power bus, the electret comprising an output having an alternating current voltage when the alternating current power bus is energized; and an indicator comprising an input electrically interconnected with the output of the electret and an indication output responsive to the alternating current voltage of the output of the electret.
It is known to use LCD indicators for medium voltage power busses; however, it is believed that this technology is limited to nominal medium voltage levels since suitably high electric field levels are needed for proper operation.
There is room for improvement in indicator apparatus for a power bus.